1. Field of the Invention
This invention relates to an inspection arrangement for a printed code symbol, in particular to the inspection of a bar code symbol.
2. Description of the Prior Art
In an improved checkout system for self-service stores, the packages of the products for sale are provided with a universal product code symbol which provides information enabling the price of the item to be printed and displayed through a computer controlled system. The universal product code consists of a rectangular pattern of parallel bars, the bars being of predetermined widths and at predetermined distances apart. The relative widths of the bars and their spacing provides information with respect to the name of the product, its manufacturer and the package size. At the checkout stand, the code symbol is scanned as the package is conveyed through a reader, feeding a signal to a computer programmed with pricing data for various products and their package sizes. The computer then transmits a signal causing a display of the price of the item and an imprinting of a tape that forms a receipt for the purchaser. This system is very efficient, reducing the labor requirements for market checkout stands, as well as speeding up the checkout operation and insuring greater accuracy.
An essential part of the system is an accurate reproduction of the proper code symbol on each package. When the package is printed it is necessary that the bars of the code symbol be imprinted within closely defined spacing tolerances and that the various bars have widths within permissible maximum and minimum dimensions. If this is not adhered to, the symbol cannot be read properly and the automatic system will not function.
Various conditions will affect the nature of the bars imprinted. The viscosity of the ink used has a direct bearing on the widths of the bars printed in the code symbol. Thinner inks will spread more than thicker inks. The material of the package also influences the bar width. Some materials are more porous than others to provide variations in the flow of the ink. Also, the pressure achieved in the printing operation, to some extent dependent upon the thickness of the package material, will have a bearing upon the widths of the bars produced in the symbol.
Accordingly, it is necessary to make periodic inspections of packages as they are printed to make certain that the universal product code symbols remain within permissible tolerances. In the past, this has been possible only by a meticulous inspection of the code symbol through the use of an optical comparator. This not only requires the expense of a comparator when the inspection is to be made, but also is a very tedious, slow and expensive operation.
Bar code symbols are coming into other and more widespread use outside of retail stores, such as in inventory control, with similar problems in assuring accurate reproduction of the code symbol.